Nanostructured meta-materials and meta-surfaces to collimate light emissions from leds

ABSTRACT

A system, method and device for collimating the output of a light emitting diode (LED) are disclosed. The system, method and device include an LED substrate including a top surface from which the light is emitted, and an array of subwavelength scattering antennas positioned within the emitted light path, the array of subwavelength scattering antennas configured to select directions of scatter of the LED emitted light to provide collimated light output from the device. The array may be aligned perpendicular to the plane of propagation of the light emitted from the LED and may be positioned adjacent to the top surface. The array may be at least partially, or completely, positioned within the LED substrate. The array may be spaced a distance from the top surface and the spacing may be achieved using a dielectric spacer adjacent to the top surface. The array may be positioned within the dielectric spacer.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/573,372 filed Oct. 17, 2017, entitled “Nanostructured Meta-Materialsand Meta-Surfaces To Collimate Light Emission from LEDS”, and EuropeanPatent Application No. 18158381.6 filed 23 Feb. 2018, both of which areincorporated by reference as if fully set forth.

FIELD OF INVENTION

The present invention is related to methods of and systems forcollimating light emissions from light sources, and more particularly,to nanostructured meta-materials and meta-surfaces to collimate lightemission from light emitting diodes (LEDs).

BACKGROUND

A standard light emitting diode (LED) die typically has a Lambertianangular emission pattern regardless of emitted wavelength. For certainLED applications, there may be a benefit or need to substantiallycollimate the light emitted by LEDs. For example, the light emitted frominfrared (IR) LED's used for iris scanning needs to be collimated. Thesystems used to provide the collimated light emission use lenses coupledto the LEDs to collimate the beam in the far-field. The lenses are usedsince a typical LED has a Lambertian angular distribution of emittedlight, the lenses collimate the light outputted from the LED. Such alens or other type of optical assembly is generally a differentcomponent and/or part from the LED die. This additional part requiresintegration into the package that holds the LED in place. Often, thelens is a molded plastic part, but the collimating optics can also be areflective surface or a combination of both reflectors and lenses. Theuse of an external lens assembly increases the size of the lightemitting assembly. For example, for a typical IR LED, the package, whichis the LED along with reflector and/or plastic lens, is typically about3 mm in height. The LED die including the substrate is generally only afew 100 microns thick. The ratio of package thickness to LED diethickness is about 10 for existing commercial IR LEDs. As IR LED's areincreasingly being used in smartphones as part of modules, such as irisrecognition modules, and smartphones are continuously being made thinnerwith increasing component density, it is important to reduce thethickness of IR LEDs. A need therefore exists for a technology to allowfor LEDs emitting collimated light having a thinner profile, reduce theneed for external lenses to collimate light, narrow the radiationprofile emitted by LEDs, and to increase efficiency in coupling light toexternal optics.

SUMMARY

A system, method and device for collimating the output of a lightemitting diode (LED) are disclosed. The system, method and deviceinclude an LED substrate including a top surface from which the light isemitted, and an array of subwavelength scattering antennas positionedwithin the emitted light path, the array of subwavelength scatteringantennas configured to alter the phase and amplitude of scatter of theLED emitted light to provide collimated light output from the device.The array may be aligned perpendicular to the plane of propagation ofthe light emitted from the LED and may be positioned adjacent to the topsurface. The system, method and device may also include an embeddingmedium which the array is positioned within. The array may be at leastpartially, or completely, positioned within the LED substrate. The arraymay be spaced a distance from the top surface and the spacing may beachieved using a dielectric spacer adjacent to the top surface. Thearray may be positioned within the dielectric spacer. Alternatively, thearray may be a discrete element.

The system, method and device may include a second array ofsubwavelength scattering antennas positioned within the emitted lightpath, the second array of subwavelength scattering antennas configuredto select directions of scatter of the LED emitted light to providecollimated light output from the device. The array and the second arraymay be spaced a distance apart. The array and the second array may bethe same or different arrays.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding can be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1 illustrates an arrangement of subwavelength scattering antennasplaced on top of LED die functioning to collimate the light emitted bythe LED in the far-field;

FIG. 2 generally illustrates example arrangements of arrays ofsubwavelength scattering antennas including FIG. 2a where the array isplaced on top of the LED top surface, FIG. 2b where the array issubmerged and/or partially submerged in/on the LED top surface, and FIG.2c where the array is offset from the LED top surface using a dielectricspacer placed between the array and the LED top surface;

FIG. 3 generally illustrates example arrangements of arrays ofsubwavelength scattering element including FIG. 3a where the array isplaced on top of an LED top surface, FIG. 3b where the array is placedon the top surface of an LED with z offsets between individualscattering antennas, FIG. 3c where multiple arrays are placed on the LEDsurface with each array having different arrangement of scatteringantennas without gaps between each of the layers, and FIG. 3d wheremultiple arrays are placed on the LED surface with each array havingdifferent arrangement of scattering antennas with dielectric spacersbetween layers of designed thicknesses;

FIG. 4 illustrates a method of collimating the light output from an LEDsubstrate;

FIG. 5a illustrates an example of application of scattering antennas tocollimate light from an LED;

FIG. 5b illustrates a device designed as an LED with bulk reflectivematerial and no phosphor layers;

FIG. 5c illustrates an LED with a side reflective coating and nophosphor;

FIG. 5d illustrates an LED with a bulk reflective material and aphosphor layer;

FIG. 5e illustrates an LED with side reflective coating and a phosphorlayer;

FIG. 6 illustrates a plot of the phase distribution ϕ(x,y) of thescattering antennas over the LED size of 1 mm×1 mm;

FIG. 7 illustrates a plot of the phase distribution ϕ(x,y) of thescattering antennas over a smaller area of 25 um×25 um (smaller whencompared to the dimensions of the LED which are typically 1-2 mm perside as shown in FIG. 6);

FIG. 8 illustrates a plot of the phase function of the scatteringantennas;

FIG. 9 illustrates a top view of the arrangement of the scatteringantennas over a smaller area of 10 um×10 um on a sapphire substratecorresponding to the phase distribution plot of FIG. 7;

FIG. 10 illustrates a zoomed-in image of the scattering antennas; and

FIG. 11 illustrates a further zoomed-in image of the scatteringantennas.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth,such as particular structures, components, materials, dimensions,processing steps, and techniques, in order to provide a thoroughunderstanding of the present embodiments. However, it will beappreciated by one of ordinary skill of the art that the embodiments maybe practiced without these specific details. In other instances,well-known structures or processing steps have not been described indetail in order to avoid obscuring the embodiments. It will beunderstood that when an element such as a layer, region, or substrate isreferred to as being “on” or “over” another element, it can be directlyon the other element or intervening elements may also be present. Incontrast, when an element is referred to as being “directly on” or“directly” over another element, there are no intervening elementspresent. It will also be understood that when an element is referred toas being “beneath,” “below,” or “under” another element, it can bedirectly beneath or under the other element, or intervening elements maybe present. In contrast, when an element is referred to as being“directly beneath” or “directly under” another element, there are nointervening elements present.

In the interest of not obscuring the presentation of embodiments in thefollowing detailed description, some structures, components, materials,dimensions, processing steps, and techniques that are known in the artmay have been combined together for presentation and for illustrationpurposes and in some instances may have not been described in detail. Inother instances, some structures, components, materials, dimensions,processing steps, and techniques that are known in the art may not bedescribed at all. It should be understood that the following descriptionis rather focused on the distinctive features or elements of variousembodiments described herein.

Artificially structured, sub-wavelength, nanostructured opticalmeta-materials, meta-surfaces and photonic crystals with spatialvariation of nano-scale structural and chemical properties collimatelight emitted from planar light emitting devices such as light emittingdiodes (LEDs) to provide flat, ultra-thin, compact LEDs capable ofemitting collimated light into the far-field without the use ofreflector and/or lens assembly. In certain applications, such as cameraphones and miniaturized personal electronics devices, the thickness ofLED's with reflectors and lens can be an important limitation. Thepresent collimation optics may be built on the LED chip itself insteadof requiring a separate optical assembly.

The proposed method reduces the thickness of LEDs (not limited to IRLEDs but also applicable to visible LEDs) by incorporating subwavelengthnanostructures into the LED architecture. The subwavelengthnanostructures may be sized smaller than free space wavelength of lightin lateral size (x,y), and the z-height, along direction of propagationmay or may not be sub-wavelength. For resonant implementations, z mayalso be subwavelength. For the non-resonant implementations, z may besubwavelength or may be approximately one wavelength in size.Subwavelength references a reference wavelength, such as at a specifieddesign wavelength. These subwavelength nanostructures affect theamplitude and phase of the light illuminating them and cause the lighttransmitted or scattered by an array or arrays of the nanostructures tobe collimated in the far-field of the LED. These subwavelengthnanoparticles collectively behave as an optical collimating element oras a thin, flat optical lens used to collimate the light output from theLED. This eliminates the need for an external reflector and lenscombination, thereby dramatically reducing the thickness of the LEDpackage. The subwavelength nanostructures may be referred to herein asscattering elements and/or scattering antennas.

FIG. 1 illustrates an arrangement 100 of subwavelength scatteringantennas or nanostructures placed on top of an LED die 110 functioningto collimate the light emitted by the LED in the far-field. Thearrangement 100 of subwavelength scattering antennas may form an arrayof subwavelength scattering antennas 120. The LED die 110 produces lightthat has a Lambertian angular emission pattern. While FIG. 1specifically depicts the LED die 110, the description herein includes,as would be understood by those possessing an ordinary skill in the art,a phosphor placed above the LED die 110 with the array 120.

An embedding medium 130 may be coupled to the LED die 110. Thisembedding medium 130 may take the form of a dielectric including, butnot limited to, a silicon, such as polydimethylsiloxane (PDMS), a glassor acrylic, such as polymethyl methacrylate (PMMA), and silicon dioxide.The embedding medium 130 is designed to provide a host medium for eachlayer when using multiple layers. The general purpose for the embeddingmedium 130 is to mechanically hold the nanostructures. For example ifthe nanostructures are implemented as nanoparticles which are notfabricated by lithography techniques, the embedded medium 130 acts as ahost medium. The embedding medium 130 may be a medium with tunableproperties, such as liquid crystals, to tune the optical scatteringproperties of the nanostructures, or a medium with thermally variablerefractive index to enable tuning of the scattering properties bytemperature.

The subwavelength scattering antennas 120 may be designed within theembedding medium 130. These subwavelength scattering antennas 120 caneither be placed in the near-field or far-field of the LED emission areaand are specifically designed to interact with light emitted by thelight source. The near-field and far-field are regions of theelectromagnetic field around the led emission area. Non-radiative‘near-field’ behaviors of the emission dominate close to the ledemission area, while electromagnetic radiation ‘far-field’ behaviorsdominate at greater distances. The sub-wavelength scattering antennas120 can also be referred to as artificial electromagnetic and/or opticalmaterials. These materials may be uniquely designed to interact withlight in specific ways by engineering the structural and chemicalparameters of the scattering antennas 120. Interaction refers to thelight-matter interaction and specifically, the interaction of light andeach nanostructure. The incident electric fields may induce dipoles(electric or/and magnetic) and multipoles (electric or/and magnetic) inthe nanostructures which scatter the incident light inwell-characterized directions. The structural parameters of thescattering antennas 120 may include shape, size, and periodicity, whichmay occur in one or two axes, for example.

These subwavelength scattering antennas 120 may be formed in an arrayextending generally in the x-y plane. The scattering antennas 120 mayinclude, or may be, nanostructures. The array of scattering antennas 120may act optically with a periodic structure, which splits and diffractslight into several beams travelling in different directions. Thescattering antennas 120 may act on the amplitude and/or phase of the LEDemitted light. The direction(s) of the output light depend upon thespacing, shape and size of the scattering antennas, and the wavelengthof the light emitted by the LED. The various illustrations of thepresent system include the use of scattering antennas 120 used intransmission, although it would readily be understood that suchscattering antennas 120 may also be used in reflection.

The area A on the plane, occupied by the scattering antennas 120, ischosen to be large and intersect as much light emitted by the LED aspossible. However, the area A may be limited by the size of the LED, forexample. The operating principle of the collimation layer is as follows:the subwavelength scattering antennas 120 are arranged as an array onthe surface such that some of the structural attributes of thescattering antennas 120 vary spatially with the area A or by parts ofthe area A. The structural attributes may include: sizes in anydimension, shapes in any dimension and spacing between neighboringsubwavelength scattering antennas 120, or a combination thereof.

The shape may include rectangles, squares, pyramids, triangles, cubiods,cylinders and other shapes with 2D cross-sections including square,rectangular, circular, elliptical, hexagonal and the like. The shapesmay include a varying size as the scattering antennas 120 proceedoutward from the center of the LED die as shown, for example. The shapemay vary with a structural parameter, for example the side or radius asa function of (x,y). By way of non-limiting example only, the centeredscattering element may be selected to be a certain shape, with the oneimmediately adjacent thereto, in both axes, be 110% of the size in thez-axis with the same footprint in the x and y axes. This pattern maycontinue until the edge of the LED die 110.

The size may include various dimensions of the aspects of the scatteringantennas 120 and may be designed to interact with the light from the LEDdie 110 in specific ways. The size may vary with a structural parameter,for example the side or radius as a function of (x,y). By way of exampleonly, the center structure of the scattering antennas 120 may be thelargest in x and y axis footprint, and then each structure progressingoutward therefrom may have an x/y axis footprint of 90% until the edgeof the LED die 110 is reached.

The periodicity of the scattering antennas 120 may also be varied. Thevariation may include changing the periodicity of the scatteringantennas 120 by a certain factor either creating additional spacing orshrinking the spacing of progressive scattering antennas 120 radiatingoutward to the edge of the LED die 110. The scattering antennas 120 maybe arrayed with suitably designed periodicities in the x,y spatialdimensions. The scattering element may include nanostructures withcertain periodicity in the z-direction, such as hyperbolicmetamaterials, for example.

The chemical parameters of the scattering antennas 120 may include thematerials used. As would be understood by those possessing an ordinaryskill in the art, the chemical variation in the scattering antennas 120may enable a selection of refractive index and loss for scattererthereby changing scattered light amplitude and phase. Such a variationmay be used in the design of the subwavelength scattering antennas 120to produce the appropriate effect on the light emitted from the LED die110.

Examples of devices that use these subwavelength scattering antennas 120include meta-materials, photonic crystals and meta-surfaces. The choiceof materials could include, but not limited to, metals (including butnot limited to gold, silver, copper, aluminum) and dielectrics(including but not limited to silicon, silicon dioxide, titaniumdioxide, gallium arsenide, aluminum gallium arsenide) and hybridmetallo-dielectric material combinations used to achieve low-lossplasmonics in the visible wavelength regime. These subwavelengthscattering antennas 120 collectively behave as an optical collimatingelement. This eliminates the need for an external reflector and lenscombination thereby dramatically reducing the thickness of the LEDpackage.

The implementation of the arrangement of the subwavelength scatteringantennas 120, as well as the shape, size and material properties of eachelement in the array may be dependent on the position of the array withrespect to that of the LED top surface and the desired outputcollimation profile, the range of operating wavelengths and also anyfabrication considerations and restrictions. Due to the variation in theoptical field distribution away from the emitter region of LED, (withthe field distribution at any plane a function of the x,y,z position ofthe plane), the interaction of the array with the photons incident onthereon will vary and be a function of the z position of the scatteringantennas 120. Therefore, a particular design may be adapted to collimatelight by varying its structural and material properties depending on thedistance of the scattering element array from the LED emitter regionwhile considering reflections from the LED top surface.

Each subwavelength scattering element 120 behaves as a nanoscale antennaand scatters incident light, from a certain range of incident angles, tocertain directions with known amplitudes and phases. The scatteringantennas as a group may be designed to select directions of scatter, orotherwise cause directions of scatter, to provide collimated lightoutput. By suitably arranging a large number of such scattering antennason or close to the surface of an LED in the z-axis, the light incidenton the array of subwavelength scattering antennas 120 can be collimatedto the far-field. The design of the subwavelength scattering antennas120 with spatially varying parameters is dependent on the knowledge offield distributions of the light incident on the scattering elementarray. The subwavelength scattering antennas array 120 behaves opticallyas a nanoscale collimating thin film lens used to collimate the lightemitted by the LED.

FIG. 2 illustrates several example arrangements of arrays ofsubwavelength scattering antennas including FIG. 2a where the array 220is placed on top of the LED 210 top surface, FIG. 2b where the array 260is submerged and/or partially submerged in or on the LED 250 topsurface, and FIG. 2c where the array 290 is offset from the LED 280 topsurface using a dielectric spacer 285 placed between the array 290 andthe LED 280 top surface.

In FIG. 2a , the array of subwavelength scattering antennas 220 iscoupled to the LED 210 top surface. That is, the array 220 is placedadjacent in the z-axis to the surface of the LED 210 in an embeddingmedium 230. The spatial positioning of the array 220 adjacent to the topsurface of the LED 210 may be used to as a group to select directions ofscatter, or otherwise cause directions of scatter, to provide collimatedlight output. Additionally, this spatial positioning may provide furtherbenefits including other beamforming configurations.

In FIG. 2b , the array of subwavelength scattering antennas 260 issubmerged, either completely or partially, in or on the LED 250 topsurface. That is, the array 260 is placed within or partially within theLED 250 top surface in the z-axis direction covered by or partiallycovered by an embedding medium 270. This spatial positioning of thearray 260 at least partially, or completely, within the LED 250substrate may be used to select directions of scatter, or otherwisecause directions of scatter, to provide collimated light output. Inparticular, placing the array 260 within or partially within the LED 250substrate may eliminate or at least control with respect to spuriousscattering, and other inputs into the collimation design, from the LED250 top surface.

In FIG. 2c , the array of subwavelength scattering antennas 290 isoffset from the LED 280 top surface. This offset may be in the z-axisdirection. The offset may occur by placing a dielectric spacer 285between the array 290 and the LED 280 top surface in the z-axis in anembedding medium 295. The thickness in the z-axis, denoted as h, of thedielectric spacer 285 may determine the positioning in the z-axis of thearray 290. This spatial positioning of the array 290 spaced apart fromthe LED 280 substrate may be used to select directions of scatter, orotherwise cause directions of scatter, to provide collimated lightoutput. In particular, spacing the array 290 from the LED 280 topsurface using a dielectric spacer 285 may control the input ofreflections from the LED 280 top surface and may enable another factorinto the process by selection of the dielectric spacer 285. The spacer285 may be utilized to aid in the fabrication of the assembly, forexample in a configuration where the lens is to be fabricated on top ofthe phosphor.

This choice of the dielectric spacer 285 size and material providesadditional variables that may be adjusted to provide or enhance thecollimation in the far field of the produced light. The choice of thedielectric material may also enable a better transition with theembedding medium 295, thereby operating as a transition from the LED 280substrate to embedding medium 295 instead of the situation in FIG. 2awhere the embedding medium 230 and LED 210 substrate as substantiallycontacting and produce an interface that the light propagates through.As would be understood, such spacing may consume additional space in thepackage. Additionally, this spatial positioning may provide furtherbenefits including an improvement in extraction efficiency of light fromthe LED.

Additionally, scattering antennas may be arranged in multiple layers(not shown) with the possibility of dielectric spacers between layersdesigned to aid in the selection of light scatter. The additional layersmay be used to provide operation over broad parameter ranges bysplitting some parameters into each layer where parameter may bewavelength and/or polarization, for example, correction of anyaberration errors, and addition of any multi-functionality to thecollimating structure.

Some or all of the successive layers of scattering antennas may also beplaced directly adjacent to other layers. The individual scatteringantennas may have offsets in the z-axis with other scattering antennas,although generally, scattering antennas lie on a plane parallel to theLED top surface. FIG. 3 illustrates several example arrangements ofarrays of subwavelength scattering element including FIG. 3a where thearray 320 is placed on top of LED 310 top surface, FIG. 3b where thearray 340 is placed on top surface of LED 330 with z offsets betweenindividual scattering antennas, FIG. 3c where multiple arrays 360,370are placed on the LED 350 surface with each array having differentarrangement of scattering antennas without gaps between each of thelayers, and FIG. 3d where multiple arrays 390,395 are placed on LED 380surface with each array having different arrangement of scatteringantennas with dielectric spacers 385 between layers of designedthicknesses.

FIG. 3a illustrates a single array of scattering antennas 320 positionedadjacent to the top surface of the LED 310 substrate. This provides abase example from which the additional examples of FIG. 3 are derived asthe gaps between different arrays can be zero or greater than zero.

FIG. 3b illustrates a single array of scattering antennas 340 where onesof the scattering antennas within the array are displaced to differentpositions (incorporating z-axis offsets) within the light output fromthe LED. As is shown in FIG. 3b , several of the scattering antennas 340are partially submerged within the LED 330 substrate. As would beunderstood, although not shown, ones of the elements may be completelysubmerged in the LED 330 substrate. Several of the scattering antennas340 are positioned adjacent to the LED 330 substrate, similar to theirrespective position in FIG. 3a . Several of the scattering antennas 340are also displaced in the z-axis a distance from the top surface of theLED 330 substrate. Others of the scattering antennas 340 are displacedin the z-axis to a different distance from the top surface of the LED330 substrate.

FIG. 3c illustrates multiple arrays of scattering antennas 360,370 (twoarrays are shown) placed on the LED 350 v top surface with each arrayhaving a different arrangement of scattering antennas, although the samearrangement may be used, without gaps between the arrays. Generally, thefirst array 360 may be positioned identically to that depicted in FIG.3a . The second array 370 may be positioned adjacent to the first array360.

FIG. 3d illustrates multiple arrays of scattering antennas 390,395(again two arrays are shown). Each array 390,395 may have a differentarrangement of scattering antennas, although the same arrangement may beused. Generally, the first array 390 may be positioned identically tothat depicted in FIG. 3a . The second array 395 may be positioned offsetfrom the first array 390 in the z-axis by a distance h₁. If more arraysare used, the spacing between arrays may be the same or may vary such asby including a distance h₂ between the second and third arrays, forexample

FIG. 4 illustrates a method 400 of collimating the light output from anLED substrate. The method includes the steps of identifying the LEDoutput and LED substrate top surface at step 410. The method furtherincludes providing an array of subwavelength scattering antennas tointeract with the light output by the LED at step 420. The method mayinclude arranging the scattering antennas in the z-axis to provide anappropriate interaction with the light to product collimated light inthe far-field at step 430. The method may include varying the mediumwhere the scattering antennas are embedded from the selection of the LEDsubstrate, an embedding medium and a dielectric spacer, and includingpartial embedding within this substrate at step 440. The method may alsoinclude varying the size and/or shape of the scattering antennas toprovide the desired effect of the output light at step 450. The methodmay also include varying the material of the scattering antennas toprovide the desired effect of the output light at step 460.

The scattering antennas are designed in such a way that the light at thefar-field of the LED is (substantially) collimated when compared to anLED without the scattering antennas. Each element may be selected tocause the scattering to impart a certain amplitude and phase to thelight. Therefore, the scattering antennas may be implemented using manydifferent designs.

The scattering antennas may be broadly categorized based on mode ofoperation as a resonant scatterer or a non-resonant scatterer. Aresonant scatterer supports an electromagnetic resonance for a given setof structural, material parameters and a given wavelength. For example,the scattering antennas may support Mie resonances including electricand magnetic dipole and quadrapole resonances. By way of example, suchscattering antennas may include silicon nanopillars supporting bothelectric and magnetic dipoles.

Alternatively, the scattering antennas may be a non-resonant scatterer.This scattering element may affect the amplitude and phase of thescattered light by different means, like, for example, by use ofwaveguiding modes. In this case, each scattering element may provide adifferent phase shift to the incident wave as it propagates through thescattering antennas. The scattering antennas as a whole tune theamplitude and phase of the incident wave as it propagates through thearray. In both cases, the amplitude and phase variations in thescattered field may be obtained by, for example, varying the dimensionsof the scattering antennas based on a certain pattern or profile.

A series of examples of application of scattering antennas to collimatelight from an LED are illustrated in the collectively referred to FIG.5. In FIG. 5a , the LED architecture may include a semiconducting layer502, such as gallium nitride (GaN) and a sapphire substrate 504.Although not shown in FIG. 5a , a phosphor layer may also be includedbetween the sapphire substrate 504 and the scattering antennas 506. Inthe final device, the emitted light exits from the semiconducting layer502 into the sapphire substrate 504 and finally to the ambient medium.As shown in FIG. 5a , the scattering antennas 506 may be disposed on topof the sapphire substrate 504. In FIG. 5a , the sapphire substrate 504is larger than the size of the semiconductor layer 502.

The scattering antennas 506 may include a high dielectric constant (orhigh refractive index) and low loss material, such as titanium dioxide,gallium nitride, silicon nitride, amorphous or crystalline silicon atnear IR wavelengths, and the like, for example. The low loss propertiesof the materials provide high transmission efficiency for the device.Titanium dioxide may be used as the material to implement non-resonantscattering antennas 506. The refractive index of the material toimplement the scattering antennas 506 may have a refractive index of atleast 2.5 with a loss less than 1×10⁻³.

Specifically, the scattering antennas 506 may include titanium dioxidefor use at wavelengths of 450 nm and 620 nm with a refractive index ofapproximately 2.5 with loss less than 1×10⁻³ Alternatively, silicon maybe utilized as the scattering antennas 506 for near infrared (NIR)applications in mobile devices (such as for face recognition and irisrecognition, for example) with a refractive index of approximately 3.66(in the range of 3.6 to 3.7) and loss less than 3×10⁻³.

The scattering element pattern may be arranged in rectangular orhexagonal lattices. In the example of FIG. 5a , the pattern may bearranged in a rectangular lattice. The lattice period may be smallerthan 400 nm. In the example of FIG. 5a , the lattice period may be 250nm. The radius of the rods within the scattering antennas may vary from40 nm to 110 nm. The upper and lower bounds of the radii used may bedictated by fabrication tolerances and the design may be varied toaccommodate fabrication tolerances. In the non-resonant device design,the height of the scattering antennas 506 may be several 100 nm andlimited by rod aspect ratio that may be achieved through practicalmeans. In one particular design, the height of the nanostructures may beless than 700 nm. This particular design may have a wavelength centeredon 620 nm. The design concepts may be extended to other wavelengthsincluding visible light for both narrow band and broadband (white light)operation. In the example, the thickness of the sapphire substrate 504may be selected to be 100 um, but as would be understood from thepresent description, the thickness may be varied and limited byfabrication and handling procedures. The choice of different materialsand fabrication process may allow for use of thinner materials for thesubstrate 502. In one example, the focal length of the collimatingnanostructure array 506 may be defined to be 100 um. The focal lengthmay be designed to structure images of the active light regions of theLED chip.

In the examples of FIG. 5, the radius of the rods may be varied as afunction of position (x,y) along the sapphire substrate. The rod radiusmay be varied as function of (x,y) such that the resulting light in thefar-field is collimated. Alternatively, instead of varying the radius as(x,y), the radius may be held constant and height may be varied as afunction of (x,y). This design results in the array of scatteringantennas 506 functioning as a collimating lens. The radii of thetitanium scattering antennas 506 may be selected to provide an overallphase distribution ϕ(x,y) of the structure resembling that of acollimating lens. This affect may be achieved by choosing to vary theradius of each rod in the array of scattering antennas 506 to controlthe amplitude and phase of the light scattered by the rod.

By way of example only, designs of the non-resonant scattering antenna506 may include both rectangular and hexagonal lattice with one antennaper unit cell. The structure may be fabricated on top of the sapphiresubstrate 504 with a background medium of air. The focal length may bedesigned to structure images from the active light emitting regions ofthe LED chip. For example, there may be a device 500 designed at 450 nmwith a periodicity of 250 nm using titanium dioxide non-scatteringantennas 506 of height 600 nm with the radii varying spatially from 25nm to 110 nm. Another design at 620 nm may be used for the red coloremitting LEDs that emit red without use of phosphor. Such a device 500may include a periodicity of 300 nm with titanium dioxide non-scatteringantennas 506 of height 700 nm with radii varying spatially from 25 nm to130 nm.

By way of additional examples, designs of the resonant scatteringantenna 506 may include both rectangular and hexagonal lattice with oneantenna per unit cell. The operating wavelength may be 850 nm with aperiodicity of 400 nm using rods of height 150 nm with radii varyingfrom 25 nm to 180 nm. A glass substrate may be used.

These antenna layers can reduce the need for external lens to collimatelight, be used to narrow the radiation profile emitted by the LED inorder to provide increased efficiency in coupling light to externaloptics to thereby improving the overall system efficiency. Thistechnique may be applied to applications for existing LED structureswhich use either bulk reflective material or thin reflective layers onthe side of the LED.

FIG. 5b through FIG. 5e provide additional examples of devicesincorporating the scattering antennas. In FIG. 5b , there is a device520 designed as an LED with bulk reflective material and no phosphorlayers. Device 520 includes a bulk reflective material 522 positioned atthe ends of the core of the device 520. The core of the device 520includes a sapphire substrate 524 that is situated between a LED chip526 and scattering antennas (nanostructured layer) 528. The LED 520emits light at certain colors/wavelengths, such as InGaN LEDs emittingblue, green color.

FIG. 5c illustrates an LED 540 with a side reflective coating 542 and nophosphor. Device 540 includes a side reflector 542 positioned at theends of the core of the device 540. The side reflector 542 may include abragg grating, dielectric mirrors, metallic mirrors, for example. Thecore of the device 540 includes a sapphire substrate 544 that issituated between a LED chip 546 and scattering antennas (nanostructuredlayer) 548. The LED 540 emits light at certain colors/wavelengths, suchas InGaN LEDs emitting blue, green color.

The nanostructured layers 548 may be applied to the top of the phosphor550 in order to collimate the light emitted from the phosphor 550. Thephosphor 550 may be selected to emit broadband yellow light (as in thecase of white LED—white is blue+yellow) or completely convert all bluelight from LED chip 546 to emit in a narrow band of wavelength/s (forexample LEDs that emit amber, deep red colors). The nanostructure layer548 can be designed to either collimate white light (yellow+blue) orcertain specific colors/wavelengths.

FIG. 5d illustrates an LED 560 with a bulk reflective material 562 and aphosphor layer 570. Device 560 includes bulk reflective material 562positioned at the ends of the core of the device 560. The core of thedevice 560 includes a sapphire substrate 564 that is situated between aLED chip 566 and phosphor layer 570 and scattering antennas(nanostructured layer) 568 may be adjacent to phosphor layer 570 distalto sapphire substrate 564. Additional silicone wings 572 may be utilizedunderlying the phosphor layer 570 extending beyond the sapphiresubstrate 564 and LED chip 566.

The nanostructured layers 568 may be applied to the top of the phosphor570 in order to collimate the light emitted from the phosphor 570. Thephosphor 570 may be selected to emit broadband yellow light (as in thecase of white LED—white is blue+yellow) or completely convert all bluelight from LED chip 566 to emit in a narrow band of wavelength/s (forexample LEDs that emit amber, deep red colors). The nanostructure layer568 can be designed to either collimate white light (yellow+blue) orcertain specific colors/wavelengths.

FIG. 5e illustrates an LED 580 with side reflective coating 582 and aphosphor layer 590. Device 580 includes a side reflective coating 582positioned at the ends of the core of the device 580. The side reflector582 may include a bragg grating, dielectric mirrors, metallic mirrors,for example. The core of the device 580 includes a sapphire substrate584 that is situated between a LED chip 586 and phosphor layer 590 andscattering antennas (nanostructured layer) 588 may be adjacent tophosphor layer 590 distal to sapphire substrate 584.

FIG. 6 illustrates a plot 600 of the phase distribution ϕ(x,y) of thescattering antennas over the LED size of 1 mm×1 mm. FIG. 7 illustrates aplot 700 of the phase distribution ϕ(x,y) of the scattering antennasover a smaller area of 25 um×25 um (smaller when compared to thedimensions of the LED which are typically 1-2 mm per side as shown inFIG. 6). FIG. 6 and FIG. 7 collectively illustrate how the wave isretarded at different location (x,y) and further demonstrate that thereis a collimated beam or otherwise may demonstrate beam forming.

FIG. 8 illustrates a plot 800 of the phase function of the scatteringantennas. FIG. 9 illustrates a top view 800 of the arrangement of thescattering antennas over a smaller area of 10 um×10 um on a sapphiresubstrate corresponding to the phase distribution plot 800 of FIG. 8.The rod radii and arrangement have been selected to provide the behaviorof a collimating lens with a focal length of 100 um. FIG. 9 illustratesthe array of rods that approximately implements the phase distributionfunction described above. That is, the illustrated rod arrayapproximately imparts phase delays to incident light as given by thephase distribution function. In this illustration, the radius of therods may be varied as a function of position (x,y) along a substrate,such as sapphire. The rod radius is varied as a function of (x,y) suchthat the resulting light in the far-field is collimated. The resultingarray of nanostructures behaves like a collimating lens. The radii ofthe titania nanorods are chosen such that the overall phase distributionΦ(x,y) of the structure resembles that of a collimating lens. This maybe achieved by varying the radius of each rod in the array to controlthe amplitude and phase of the light scattered by the rod.

FIG. 10 illustrates a zoomed-in image 1000 of the scattering antennas.FIG. 9 illustrates the phase function of FIG. 8 and depicts how thephase function carries into the structure of the scattering antennas. Bycomparing the two figures, one readily concludes the relationship.

FIG. 11 illustrates a further zoomed-in image 1100 of the scatteringantennas. There is shown a series of rods that are arranged in periodicfashion. FIG. 11 illustrates a periodic arrangement of rods withspatially varying dimensions with the same constant height.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element can be used alone or in any combination with orwithout the other features and elements. In addition, the methodsdescribed herein may be implemented in a computer program, software, orfirmware incorporated in a computer-readable medium for execution by acomputer or processor. Examples of computer-readable media includeelectronic signals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs).

What is claimed is:
 1. A device for collimating the output of a lightemitting diode (LED), the device comprising: an LED substrate includinga top surface from which the light is emitted; an array of subwavelengthscattering antennas positioned within the emitted light path, the arrayof subwavelength scattering antennas configured to select directions ofscatter of the LED emitted light to provide collimated light output fromthe device; and a second array of subwavelength scattering antennaspositioned within the emitted light path and spaced a distance apartfrom the array, the second array of subwavelength scattering antennasconfigured to select directions of scatter of the LED emitted light toprovide collimated light output from the device.
 2. The device of claim1, wherein the array is perpendicular to the plane of propagation of thelight emitted from the LED.
 3. The device of claim 1, wherein the arrayis positioned adjacent to the top surface.
 4. The device of claim 1,wherein the second array is perpendicular to the plane of propagation ofthe light emitted from the LED.
 5. The device of claim 1, wherein thesecond array is positioned adjacent to the top surface.
 6. The device ofclaim 1, further comprising an embedding medium which the array ispositioned within.
 7. The device of claim 1, further comprising anembedding medium which the second array is positioned within.
 8. Thedevice of claim 1, wherein the array is at least partially positionedwithin the LED substrate.
 9. The device of claim 1, wherein the array ispositioned within the LED substrate.
 10. The device of claim 1, whereinthe array is spaced a distance from the top surface.
 11. The device ofclaim 1, wherein the second array is spaced a distance from the topsurface.
 12. The device of claim 1, further comprising a dielectricspacer adjacent to the top surface, the dielectric spacer providing aspacing of the array from the top surface in the direction of lightpropagation.
 13. The device of claim 8, wherein the array is positionedwithin the dielectric spacer.
 14. The device of claim 8, wherein thesecond array is positioned within the dielectric spacer.
 15. The deviceof claim 10, wherein the array and the second array are spaced adistance apart.
 16. A method for collimating the output of a lightemitting diode (LED), the method comprising: emitting light from a topsurface of an LED substrate; selecting directions of scatter of the LEDemitted light to provide collimated light output from the device usingan array of subwavelength scattering antennas positioned within theemitted light path; varying the medium in which the array is embedded;varying the shape and size of the array scattering antennas; and varyingthe material of the array of scattering antennas.
 17. The method ofclaim 16 further comprising further selecting directions of scatter ofthe LED emitted light to provide collimated light output from the deviceusing a second array of subwavelength scattering antennas positionedwithin the emitted light path and spaced a distance apart from thearray.
 18. The method of claim 17 further comprising varying the mediumin which the second array is embedded, varying the shape and size of thesecond array scattering antennas, and varying the material of the secondarray of scattering antennas.
 19. The method of claim 17 wherein thesecond array is spaced a distance in the light propagation directionfrom the array.
 20. A device for collimating the output of a lightemitting diode (LED), the device comprising: an LED substrate includinga top surface from which the light is emitted; and an array ofsubwavelength scattering antennas positioned within the emitted lightpath, the array of subwavelength scattering antennas configured toselect directions of scatter of the LED emitted light to providecollimated light output from the device.